C#笔记---动态类(Dynamic)应用

           背景: 在Coding中有时候会遇到一些需要解析的数据,可是数据的字段数量和名称未统一，我们没法定义实体类来对应。那么我们就会想到通过C#的dynamic动态类来实现，如果大家注意的话一些ORM框架里面貌似都有用到dynamic来实现一部分功能。

           一.Dynamic的基本应用

            1.1 通过.PropertyName来添加属性,和JavaScript的对象差不多.不过对于我们所要解析的数据,我们事先也许根本不知道属性名称,所以用这种方法意义不大.

dynamic myObj = new ExpandoObject();
myObj.Name = "Frank";
Console.WriteLine(myObj.Name);

          二.Dynamic自定义属性名称.

           2.1: 继承DynamicObject,里面提供了各种方法,重写后可以实现属性的添加.

    public sealed class MyExtendsObject : DynamicObject
    {
        private readonly Dictionary<string, object> _properties;

        public MyExtendsObject(Dictionary<string, object> properties)
        {
            _properties = properties;
        }

        public override IEnumerable<string> GetDynamicMemberNames()
        {
            return _properties.Keys;
        }

        public override bool TryGetMember(GetMemberBinder binder, out object result)
        {
            if (_properties.ContainsKey(binder.Name))
            {
                result = _properties[binder.Name];
                return true;
            }
            else
            {
                result = null;
                return false;
            }
        }

        public override bool TrySetMember(SetMemberBinder binder, object value)
        {
            if (_properties.ContainsKey(binder.Name))
            {
                _properties[binder.Name] = value;
                return true;
            }
            else
            {
                return false;
            }
        }
    }

2.2 通过字典来添加属性和赋值        

        public static void Main(string[] args)
        {
            dynamic myObj = new ExpandoObject();
            Dictionary<string, object> dic = new Dictionary<string, object>()
            {
                {"Name","Frank"},
                {"Age",23}
            };

            myObj = new MyExtendsObject(dic);
            Console.WriteLine(myObj.Age); //23
        }

           三.Dynamic解析XML.

            3.1 定义xml文件:

<?xml version="1.0" encoding="utf-8" ?>
<Person>
   <Name>Frank</Name>
   <Age>23</Age>
   <Address>TianFu SoftWarePark</Address>
</Person>

           3.2 继承DynamicObject

 public sealed class MyExtensXMLObj : DynamicObject
    {
        private readonly XElement node;

        public MyExtensXMLObj(XElement node)
        {
            this.node = node;
        }

        public override bool TrySetMember(SetMemberBinder binder, object value)
        {
            var elements = node.Elements().ToList();
            var currentElement = elements.FirstOrDefault(x => x.Name == binder.Name);
            if (currentElement != null)
            {
                currentElement.Value = value as string;
                return true;
            }
            else
            {
                return false;
            }
        }

        public override bool TryGetMember(GetMemberBinder binder, out object result)
        {
            var elements = node.Elements().ToList();
            var currentElement = elements.FirstOrDefault(x => x.Name == binder.Name);
            if (currentElement != null)
            {
                result = currentElement.Value;
                return true;
            }
            else
            {
                result = null;
                return false;
            }
        }
    }

           3.3 结果输出:

public static void Main(string[] args)
        {
            XElement root = XElement.Load(@"Test.xml");
            dynamic personList = new MyExtensXMLObj(root);
            Console.WriteLine(personList.Name); // Frank
        }

        四. 继承规则.

            1. 子类里面包含一个私有变量,用于存储数据. 这暂且叫做Data;

            2.TryGetMember(GetMemberBinder binder, out object result) 方法实现对数据的获取. binder.Name就是需要获取的属性的名称,result 是获取的属性值. 通过binder.Name在Data中获取到对应的属性值,传出到外面.(注意到了吧result是out参数)

            3.TrySetMember(SetMemberBinder binder, object value) 对存在的属性进行赋值. 上面的Set方法中,我都判断了binder.Name在data里面是否存在。如果不存在就无法赋值。返回false,如果外面对不存在的属性复制那么将会报错.